1. Field of the Invention
The present invention relates to an automatic light emission control system for electronic flashes, and more particularly the invention relates to a system for controlling the initiation and interruption of flashlight emission of an electronic flash connected to a camera having a TTL autoflash control function.
2. Description of the Prior Art
Automatic light emission control systems for electronic flashes heretofore known as TTL auto flashes have been designed so that after the flashlight emission of an electronic flash has been initiated in response to the shutter opening operation of a camera, the reflected light of the flashlight impinging on an object to be photographed is measured through the taking lens of the camera as the amount of light at the position of a film surface so that when the integrated value of the light amount obtained by the light measurement reaches a preset exposure discrimination level corresponding to the correct exposure, an emission interrupt signal is transmitted from the camera to the electronic flash and thus the flashlight emission of the electronic flash is interrupted immediately.
Where such a conventional system is used to control a plurality of electronic flashes, in order to obtain the desired relative emission amounts for the individual electronic flashes, the usual practice is to adopt such complicated method as causing the distances between the respective electronic flashes and an object to be photographed to differ from one .another or providing selected one or more of the electronic flashes with filters to decrease the amounts of flashlight emission thereof and these methods also have the disadvantage of being subjected to restrictions with respect to the photographing space, the kinds of filters, etc.
On the other hand, U.S. Pat. No. 4,457,602 (Mizokami), for example, discloses a multiple light emission control system utilizing a plurality of electronic flashes and in this system the amounts of flashlight emission from the individual electronic flashes can be compensated separately under the TTL autoflash control as desired by a photographer. The principle of this control is such that in the TTL photometry circuit of the camera the relative relation between the integrated value of measured light amount and the exposure discrimination level is set separately for each of the electronic flashes to differ from one another and thereby to provide the electronic flashes with separate compensation amounts which are different from one another so that as for example, the gain of the TTL photometry circuit can be increased for selected one of the electronic flashes to compensate its amount of flashlight emission so as to keep it on the underexposure side or alternatively the exposure discrimination level can be shifted in the measured light amount integrating direction to compensate the amount of flashlight emission so as to keep it on the overexposure side.
With this multiple light emission control system, however, a plurality of exposure discrimination level signals of different values relative to one another are respectively sent to the plurality of electronic flashes from the camera and therefore a plurality of signal output terminals corresponding to the number of electronic flashes to be connected must be provided on the camera side. Thus, this multiple light emission control system cannot be used with cameras other than those of special constructions having such preparations. This system is also disadvantageous in that of the plurality of electronic flashes the one whose flashlight emission is to be interrupted later is increased in the amount of flashlight emission by a light amount corresponding to the unemitted light amount of that electronic flash whose flashlight emission has been precedently interrupted, thus failing to produce a total amount of flashlight emission intended by a photographer.